This invention relates generally to gas turbine engines and more particularly to combustor dome assemblies used in such engines.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and burned for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. Combustors used in aircraft engines typically include inner and outer combustion liners joined at their upstream ends to a dome assembly. The dome assembly includes an annular spectacle plate and a plurality of circumferentially spaced swirler assemblies mounted therein for introducing the fuel/air mixture to the combustion chamber. Each swirler assembly has a deflector extending downstream therefrom for preventing excessive dispersion of the fuel/air mixture and shielding the spectacle plate from the hot combustion gases of the combustion chamber.
Typically, the swirler assemblies, deflectors and spectacle plate are joined together by a technique such as brazing. In one conventional dome assembly, the outer diameter of the swirler assembly is brazed into an opening in the spectacle plate in one operation, and the deflector is brazed into the inner diameter of the swirler assembly in another operation. The manufacture of such a dome assembly requires several time consuming procedures, utilizes multiple fixtures and many expensive materials, and is relatively labor intensive. For instance, in the first operation, the swirler assembly is fixtured to the spectacle plate using a special fixture so that the swirler assembly can be tack welded to the spectacle plate. The tack weld fixture is then removed and a stop-off paste is applied to the spectacle plate. Next, a braze alloy paste is placed in the gap between the swirler assembly and the spectacle plate opening. The assembly is then heated to a temperature exceeding the braze alloy melting point such that the braze alloy melts and fills the gap. The assembly is then allowed to cool so that the braze alloy solidifies and joins the swirler assembly to the spectacle plate.
In the second operation, stop-off material and two forms of braze alloy (sinter braze tape and braze rope) are applied to the deflector. The deflector is then fixtured into the swirler assembly/spectacle plate sub-assembly using another fixture. Milk of magnesia is applied to this fixture to prevent seizing during subsequent heating. This assembly is then heated to a temperature exceeding the braze alloy melting point such that the braze alloy melts and fills the swirler assembly/deflector interface. The assembly is then allowed to cool so that the braze alloy solidifies and joins the deflector to the swirler assembly. The fixture is then removed.
Each different step, material and fixture used in these two operations increases the complexity and cost of manufacturing the dome assembly. Furthermore, the swirler assembly is not centered when inserted into the spectacle plate because there is some nominal gap to allow for braze alloy fill. This enables the swirler assembly/spectacle plate braze joint gap to be uneven around the circumference of the interface. In the worse case, the swirler assembly makes contact with the spectacle plate. Then, there is no braze gap where the contact is made, and there is an excessive gap opposite of the contact location.
This dome assembly design uses braze alloy in paste and rope form. Such materials are only 50% braze alloy, with the remainder being a binder. When the paste and rope are liquefied during the brazing steps, the binder bums off so that only the braze alloy remains to fill the braze gaps. Thus, braze alloy in paste and rope form is only 50% volumetrically efficient. The amount of braze alloy applied is difficult to accurately control because, in addition to being volumetrically inefficient, braze alloy paste is typically applied by hand using a syringe. Volumetric braze alloy control is important in forming combustor dome joints. Too much alloy will fill the gap and run over onto adjacent surfaces where cooling holes and surface enhancements may be obstructed. Too little alloy leaves voids in the braze gap creating a weak joint.
It is therefore desirable to have a combustor dome assembly that is easier, less time consuming and less expensive to manufacture.
The above-mentioned need is met by the present invention that provides a combustor dome assembly including a spectacle plate having an opening formed therein that defines an inner circumferential edge, at least one swirler assembly defining an inner cylindrical surface, and at least one deflector having an outer cylindrical surface. These components are arranged such that the outer cylindrical surface of the deflector is joined to the inner circumferential edge of the spectacle plate and to the inner cylindrical surface of the swirler assembly.
One preferred method of manufacturing the combustor dome assembly includes placing a first ring of joining material over the outer cylindrical surface of the deflector. Then, the outer cylindrical surface is inserted into the spectacle plate opening so that the first ring is sandwiched between a first surface of the spectacle plate and a shoulder formed on the deflector. A second ring of joining material is next placed over the deflector""s outer cylindrical surface, and a third ring of joining material is inserted into an annular groove formed in the inner cylindrical surface of the swirler assembly. The next step is to place the swirler assembly over the outer cylindrical surface so that the second ring is sandwiched between a second surface of the spectacle plate and an end of the swirler assembly and the third ring surrounds the outer cylindrical surface. The first, second and third rings are then heated to a temperature greater than their melting points so that they become molten joining material. The molten joining material is cooled to complete the joint.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.